For many people it is not sufficient to clean a house. The house must also smell good. Placing individual scent sources around the house may not suffice. There may be no air flow to help move the scent, and there may be no air flow from one room to another. Furthermore, the scent may not be augmented nor aided in emission by heat.
There are small devices that can be placed around the house in various locations to emit scents. This incurs refilling the scent emitting devices on a periodic scheme. This requires the frequent scampering of the housekeeper about the house to refill the devices.
So far, to the best of my knowledge there is no central device that can be added to a heating system for placing a scent emitting device at a central and sole location. Furthermore, the scent emitting devices cannot be shut off at any time.